build: Deduplicate CREATE_DIRS variable
build: Deduplicate CREATE_DIRS variable

Otherwise build system will complain about generating two exactly the
same rules for the target.

coreos/rkt,tmrts/rkt,Shashwatsh/rkt,ybubnov/rkt,il9ue/rkt,lucasallan/rkt,s-urbaniak/rkt,matthaias/rkt,s-urbaniak/rkt,jasonchaffee/rkt,joshix/rkt,ybubnov/rkt,kinvolk/rkt,jonboulle/rkt,linki/rkt,jonboulle/rkt,yifan-gu/rkt,squeed/rkt,kbrwn/rkt,joshix/rkt,endocode/rkt,s-urbaniak/rkt,endocode/rkt,intelsdi-x/rkt,monstermunchkin/rkt,rkt/rkt,akshaykarle/rkt,achanda/rkt,tmrts/rkt,Wilybald/rkt,mike1729/rkt,kbrwn/rkt,mike1729/rkt,sinfomicien/rkt,sinfomicien/rkt,sinfomicien/rkt,jakon89/rkt,shobhit85/rkt,euank/rkt,krnowak/rkt,nhlfr/rkt,markllama/rkt,yifan-gu/rkt,kinvolk/rkt,Shashwatsh/rkt,lucasallan/rkt,yifan-gu/rkt,akshaykarle/rkt,sgotti/rkt,akshaykarle/rkt,dgonyeo/rkt,matthaias/rkt,yifan-gu/rocket,alban/rkt,sstabellini/rkt,Shashwatsh/rkt,joshix/rkt,jasonchaffee/rkt,kinvolk/rkt,achanda/rkt,euank/rkt,linki/rkt,matthaias/rkt,il9ue/rkt,shobhit85/rkt,jakon89/rkt,sstabellini/rkt,dgonyeo/rkt,monstermunchkin/rkt,cab105/rkt,krnowak/rkt,blixtra/rkt,markllama/rkt,markllama/rkt,rkt/rkt,monstermunchkin/rkt,lucasallan/rkt,il9ue/rkt,jonboulle/rkt,sstabellini/rkt,lucasallan/rkt,cab105/rkt,linki/rkt,alban/rkt,euank/rkt,Wilybald/rkt,achanda/rkt,Wilybald/rkt,Wilybald/rkt,jjlakis/rkt,squeed/rkt,sgotti/rkt,blixtra/rkt,dgonyeo/rkt,krnowak/rkt,nhlfr/rkt,jjlakis/rkt,rkt/rkt,coreos/rkt,shobhit85/rkt,endocode/rkt,yifan-gu/rocket,alban/rkt,coreos/rkt,blixtra/rkt,jjlakis/rkt,intelsdi-x/rkt,jasonchaffee/rkt,squeed/rkt,kbrwn/rkt,jakon89/rkt,cab105/rkt,nhlfr/rkt,ybubnov/rkt,sgotti/rkt,rkt/rkt,intelsdi-x/rkt,tmrts/rkt,yifan-gu/rocket,mike1729/rkt,joshix/rkt,kinvolk/rkt